(一级结构与物种进化的关系)
Homology (同源性)
Primary structure and homology
Homologous(同源的)： proteins with similar AA sequences and functions are said to be homologous Homologous proteins from different species imply their evolutionary relatedness
O2-binding activity of Mb and Hb
O2-saturation curve of Mb and Hb
Mb: high affinity for O2
a simple hyperbolic curve
(直角双曲线)
Mb和Hb的氧饱和曲线
Hb: low affinity for O2 when [O2] is low
The primary structure of a protein:
determines its spatial structure is related with evolution of living things has a role in its bioactivity
Importance of primary structure in organism evolution
Hemoglobin (Hb) 血红蛋白
Hb: tetramer(四聚体), 4 subunits, α2β2 One Hb contains four heme groups Quaternary structure 具有四级结构
Hb: eight salt bonds link the 4 subunits to make Hb tightly form hydrophilic(亲水的) globular Байду номын сангаасrotein
Myoglobin (Mb) and Hemoglobin (Hb)
肌红蛋白与血红蛋白
Paradigms of protein structure and function Both are typical globular proteins 球状蛋白 Both are conjugated(偶联) with heme (血红素)
Mb and Hb
The β-subunit of Hb has tertiary structure very similar to that of Mb
Similarity: O2-binding activity Difference: Mb--storage of O2
Hb--transport of O2
Sickle-cell anemia cause 镰刀型贫血
The changes of key amino acids in its sequence result in function alteration of a protein
What is a relationship between the spatial structure of a protein and its function ?
Mb
Hb
Heme 血红素
Heme: Fe++ binds to protoporphyrin 原卟啉
His F8
Fe2+ and O2-binding
Fe2+ binds O2 reversibly (可逆)
Fe3+ does not bind O2 One heme binds one O2
molecule
Heme and Mb
Mb: one peptide with eight relatively straight segments of α-helix (A～H), with tertiary structure
The flat heme group rests in a hydrophobic pocket (疏水口袋) of Mb
大猩猩
长臂猿 猕猴
鼠
The phylogenetic tree (种系发生树)
根据细胞色素C序列的物 种差异建立的进化树:
分支顶端: 现存物种
沿分支线的数字表示物 种和潜在(假设)的祖先之 间的氨基酸变化
Primary structure related to its function 一级结构与功能的关系
Section III
Relevance of protein structure and function
(蛋白质结构与功能的关系)
The primary structure determines the spatial structure
All of the information necessary for folding the peptide chain into its native structure is contained in the AA sequence of the peptide
Relax state (R state): The binding of O2 to one Hb subunit in the T state triggers a change in conformation to the R state Some of the ion pairs that stabilize the T state are broken and some new ones are formed
The functions of a protein depend on its spatial structure
The native conformation of a protein is essential for its function
Biological activity will be lost when the spatial structure is destroyed
S-shaped curve (S形曲线)
How is the S-shaped curve of Hb formed?
Tense state (T state): subunits tightly bound with 8 salt
bonds
affinity of each subunit to O2 is lower